Horton, who hasn’t played in a game since being hit Jan. 22 against the Philadelphia Flyers, has skated since the injury, but Chiarelli said the organization felt the best option shut him down for the remainder of the season.

“We felt it just wasn’t in the long-term interest of Nathan to be having the specter hanging over him of trying to come back during this playoff season,” Chiarelli said after the team’s practice on Wednesday. “He’s made one step forward, and then two steps back and we just made the determination, upon consultation with our doctors; with Nathan, that it would be prudent to shut him down for the playoffs and continue to rehab for next year.

“It was a frustrating exercise for Nathan – it was a frustrating exercise for us because we’ve been through this rehab before with players and I’ve seen all kinds of rehab patterns now because usually, you can see when the player has color, and when he’s animated, you think he’s turned the corner,” Chiarelli added.

“And then they have a bout of post-concussion symptoms and they manifest themselves in different ways. With Nathan, sometimes it’d be just a fogginess, sometimes he wouldn’t feel right and sometimes there’d be a big headache.

"But it was always after three, four or five days of positive progress.”

Chiarelli and the Bruins have had an unfriendly history with concussions, but the B’s GM said the club's experiences with Marc Savard and Patrice Bergeron helped the organization make the best decision.

“It’s been instructive and I feel like an expert now –- I don’t really want to be an expert at it –- but you just get a sense now of having seen how these guys progress in their rehab and you pretty much know where they are,” Chiarelli said. “We’ve been...very good at dealing with these things and I feel, dating back to when Bergy first got concussed and we decided to shut him down, you just have to be cautious and that’s what we are with Nathan.”

Chiarelli said that Horton, who will take some time off for a couple of weeks before returning to rehab during off hours, was relived when he was informed of the club’s decision.

“[Horton] ultimately would have to agree with [the decision] and he did,” Chiarelli said. “I think with Nathan, he gets within the group and he looks back at his contributions this past year and last playoffs and he starts getting anxious and that probably compounds it, too.

“I think he felt a sense of relief, and again talking to Nathan over the course of the last couple of weeks, he doesn’t look bad – he looks good actually. But he gets these bouts – the fogginess doesn’t feel right and you have to be very careful.”

When pressed for a timetable on Horton’s return, Chiarelli remained optimistic his forward would be back for the start of the 2012-13 season.

However, the uncertainty surrounding of the head injury leaves room for question marks, which is why Chiarelli felt the best decision was to shut Horton down.

“Going into two weeks ago, you had asked me him playing this playoffs, I’m like, ‘You know, there’s a chance,’” Chiarelli said. “And then he had a couple of setbacks and then you have to take a step back and kind of look at the whole thing and that’s what we did.”